/**
* SHT1x Library
*
* Copyright 2009 Jonathan Oxer <jon@oxer.com.au> / <www.practicalarduino.com>
* Based on previous work by:
* Maurice Ribble: <www.glacialwanderer.com/hobbyrobotics/?p=5>
* Wayne ?: <ragingreality.blogspot.com/2008/01/ardunio-and-sht15.html>
*
* Manages communication with SHT1x series (SHT10, SHT11, SHT15)
* temperature / humidity sensors from Sensirion (www.sensirion.com).
*/
#if (ARDUINO >= 100)
#include <Arduino.h>
#else
#include <WProgram.h>
#endif

#include "SHT1x.h"

SHT1x::SHT1x(int dataPin, int clockPin)
{
_dataPin = dataPin;
_clockPin = clockPin;
}


/* ================ Public methods ================ */

/**
* Reads the current temperature in degrees Celsius
*/
float SHT1x::readTemperatureC()
{
int _val; // Raw value returned from sensor
float _temperature; // Temperature derived from raw value

// Conversion coefficients from SHT15 datasheet
const float D1 = -40.0; // for 14 Bit @ 5V
const float D2 = 0.01; // for 14 Bit DEGC

// Fetch raw value
_val = readTemperatureRaw();

// Convert raw value to degrees Celsius
_temperature = (_val * D2) + D1;

return (_temperature);
}

/**
* Reads the current temperature in degrees Fahrenheit
*/
float SHT1x::readTemperatureF()
{
int _val; // Raw value returned from sensor
float _temperature; // Temperature derived from raw value

// Conversion coefficients from SHT15 datasheet
const float D1 = -40.0; // for 14 Bit @ 5V
const float D2 = 0.018; // for 14 Bit DEGF

// Fetch raw value
_val = readTemperatureRaw();

// Convert raw value to degrees Fahrenheit
_temperature = (_val * D2) + D1;

return (_temperature);
}

/**
* Reads current temperature-corrected relative humidity
*/
float SHT1x::readHumidity()
{
int _val; // Raw humidity value returned from sensor
float _linearHumidity; // Humidity with linear correction applied
float _correctedHumidity; // Temperature-corrected humidity
float _temperature; // Raw temperature value

// Conversion coefficients from SHT15 datasheet
const float C1 = -4.0; // for 12 Bit
const float C2 = 0.0405; // for 12 Bit
const float C3 = -0.0000028; // for 12 Bit
const float T1 = 0.01; // for 14 Bit @ 5V
const float T2 = 0.00008; // for 14 Bit @ 5V

// Command to send to the SHT1x to request humidity
int _gHumidCmd = 0b00000101;

// Fetch the value from the sensor
sendCommandSHT(_gHumidCmd, _dataPin, _clockPin);
waitForResultSHT(_dataPin);
_val = getData16SHT(_dataPin, _clockPin);
skipCrcSHT(_dataPin, _clockPin);

// Apply linear conversion to raw value
_linearHumidity = C1 + C2 * _val + C3 * _val * _val;

// Get current temperature for humidity correction
_temperature = readTemperatureC();

// Correct humidity value for current temperature
_correctedHumidity = (_temperature - 25.0 ) * (T1 + T2 * _val) + _linearHumidity;

return (_correctedHumidity);
}


/* ================ Private methods ================ */

/**
* Reads the current raw temperature value
*/
float SHT1x::readTemperatureRaw()
{
int _val;

// Command to send to the SHT1x to request Temperature
int _gTempCmd = 0b00000011;

sendCommandSHT(_gTempCmd, _dataPin, _clockPin);
waitForResultSHT(_dataPin);
_val = getData16SHT(_dataPin, _clockPin);
skipCrcSHT(_dataPin, _clockPin);

return (_val);
}

/**
*/
int SHT1x::shiftIn(int _dataPin, int _clockPin, int _numBits)
{
int ret = 0;
int i;

for (i=0; i<_numBits; ++i)
{
digitalWrite(_clockPin, HIGH);
delay(10); // I don't know why I need this, but without it I don't get my 8 lsb of temp
ret = ret*2 + digitalRead(_dataPin);
digitalWrite(_clockPin, LOW);
}

return(ret);
}

/**
*/
void SHT1x::sendCommandSHT(int _command, int _dataPin, int _clockPin)
{
int ack;

// Transmission Start
pinMode(_dataPin, OUTPUT);
pinMode(_clockPin, OUTPUT);
digitalWrite(_dataPin, HIGH);
digitalWrite(_clockPin, HIGH);
digitalWrite(_dataPin, LOW);
digitalWrite(_clockPin, LOW);
digitalWrite(_clockPin, HIGH);
digitalWrite(_dataPin, HIGH);
digitalWrite(_clockPin, LOW);

// The command (3 msb are address and must be 000, and last 5 bits are command)
shiftOut(_dataPin, _clockPin, MSBFIRST, _command);

// Verify we get the correct ack
digitalWrite(_clockPin, HIGH);
pinMode(_dataPin, INPUT);
ack = digitalRead(_dataPin);
if (ack != LOW) {
//Serial.println("Ack Error 0");
}
digitalWrite(_clockPin, LOW);
ack = digitalRead(_dataPin);
if (ack != HIGH) {
//Serial.println("Ack Error 1");
}
}

/**
*/
void SHT1x::waitForResultSHT(int _dataPin)
{
int i;
int ack;

pinMode(_dataPin, INPUT);

for(i= 0; i < 100; ++i)
{
delay(10);
ack = digitalRead(_dataPin);

if (ack == LOW) {
break;
}
}

if (ack == HIGH) {
Serial.println("Ack Error 2"); // Can't do serial stuff here, need another way of reporting errors
}
}

/**
*/
int SHT1x::getData16SHT(int _dataPin, int _clockPin)
{
int val;

// Get the most significant bits
pinMode(_dataPin, INPUT);
pinMode(_clockPin, OUTPUT);
val = shiftIn(_dataPin, _clockPin, 8);
val *= 256;

// Send the required ack
pinMode(_dataPin, OUTPUT);
digitalWrite(_dataPin, HIGH);
digitalWrite(_dataPin, LOW);
digitalWrite(_clockPin, HIGH);
digitalWrite(_clockPin, LOW);

// Get the least significant bits
pinMode(_dataPin, INPUT);
val |= shiftIn(_dataPin, _clockPin, 8);

return val;
}

/**
*/
void SHT1x::skipCrcSHT(int _dataPin, int _clockPin)
{
// Skip acknowledge to end trans (no CRC)
pinMode(_dataPin, OUTPUT);
pinMode(_clockPin, OUTPUT);

digitalWrite(_dataPin, HIGH);
digitalWrite(_clockPin, HIGH);
digitalWrite(_clockPin, LOW);
}
